1. Field of the Invention
The present invention relates to an exposure device for an electrophotographic apparatus, having a laser light source which exposes an image carrier.
2. Background Art
FIG. 2 is a diagram showing a conventional exposure device having a laser light source.
A laser light source 15 is driven by a laser driving circuit 14. The laser driving circuit 14 modulates a laser beam 3 in accordance with a print information signal supplied from an external information processing apparatus. The laser beam 3 is reflected by a rotary polygon mirror 19 which is rapidly rotated in the direction of the arrow b, and, after passed through an Fθ lens 20, scans the surface of a photosensitive drum 1 serving as an image carrier. The surface of the rotated photosensitive drum 1 is repeatedly scanned to form an electrostatic latent image on the surface of the rotated photosensitive drum 1 which is uniformly charged.
In the exposure device, switching between a low resolution and a high resolution is realized by, in accordance with a resolution switch signal supplied from the external information processing apparatus, inserting or extracting a resolution switching lens 22 for switching over beam shapes for resolutions, into or from a laser optical path, and changing a rotational speed signal which is supplied to a rotary polygon mirror driving circuit 18 for driving the rotary polygon mirror 19, where a rotational speed for a high resolution is larger than a rotational speed for a low resolution.
Alternatively, another method is employed in which the laser emission time for a high resolution is made shorter than that for a low resolution, and the laser power is changed so that the exposure amount is optimized (for example, see JP-A-2002-131991).